ALIMENTARY TRACT OF THE KING SALMON 
95 
Stratum compactum . — The stratum compactiim is always present in the caeca of the 
king salmon. It is a striking structure and always stands out prominently in every 
microscopic section. Under the low magnification it appears as a broad wavy band 
extending around the circumference of the caecum and lying within the muscular and 
external to the tunica propria coat. 
The stratum is wavy in appearance, whether the section be transverse or longi- 
tudinal, but the extent of the folds which give rise to this phenomenon varies with the 
distension of the caecum. Apparently the more contracted the organ as a whole the 
deeper the sinuosities of the stratum compactum. The stratum is a fairly uniform band, 
i. e., its thickness is relatively constant, varying between 12 and 16 fi. 
Its structure has been described in other forms by several investigators, notably 
Mall.® Gulland ^ says that “a well-marked stratum compactum” is present in the 
Atlantic salmon. In the king salmon the stratum compactum is a homogeneous layer 
of fibrous connective tissue. It gives a characteristic staining with Mallory’s connective 
tissue stain, but shows no fibrillar structure. On its surface the stratum of the caeca 
gives rise to a few smaller strands which extend out into the tunica propria on the one 
hand and form the network extending to the circular muscle coat on the other. These 
strands, especially in the latter case, form a supporting network for the special granule 
cells of the region. No nuclei are present in the body of the stratum compactum, but 
lying along its surface, especially on the surface next the tunica propria, a few nuclei 
are found. These nuclei are irregularly ovoid in shape, and appear to be embedded in 
a thin layer of tissue l}dng on the surface of the homogeneous portion of the stratum 
compactum. This layer stains a trifle more intensely than does the main body of the 
layer. 
The stratum compactum is not present in the alimentary tract of all fishes, and 
why it should be so prominent a structure in the case of the king salmon remains a 
question. The coat is dense and it forms an uninterrupted layer (except where blood 
vessels penetrate from the outer to the inner structures of the caecum). When a caecum 
is widely distended the stratum is comparatively even and smooth in appearance. 
When the caecum is contracted it is thrown into deep sinuous folds, no matter in what 
plane the section may lie. Its function is probably best explained by Oppel,*^ who 
suggests that this is the supporting membrane for the structures of the entire organ. 
The fact that the stratum compactum is a homogeneous uninterrupted sheet seems to 
have further significance than that assigned b}^ Oppel. The fat studies described in 
a later paper suggest that this structure may be concerned in the process of the absorp- 
tion of the food products by the caecum. 
Stratum granulosum . — The caeca have a characteristic layer of granule cells bearing 
the usual relations to the stratum compactum and its network, i. e., the relation described 
“ F. P. Mall: Reticulated tissue and its relation to the connective tissue fibrils. The Johns Hopkins Hospital Reports, 
vol. I, 1896. Baltimore. 
Baton, D. Noel: Investigations of the life history of salmon, art. 3, The minute structure of the digestive tract of the salmon, 
and the changes that occur in it in fresh water, by G. Lovell Gulland. Report of the Fisheries Board for Scotland, 1898. 
c Oppel, A.: Beitrage zur Anatomic des Proteus anguineus. I. Vom Verdamuigstraktus. II. Von den Lungen. Archiv, 
fiir mikroskopische Anatomic, bd. 34, 1889, p. 511-573. 
